One route of administration for therapeutic compounds is through the skin. The skin is also one of the more efficient routes for delivery of a therapeutic compound when compared to other standard delivery routes such as oral or pulmonary delivery.
Administration to the skin is most commonly undertaken using a needle and syringe as a delivery system with the therapeutic compound in a liquid form.
Such a system has a number of associated problems including the pain and fear associated with needles, the fact they are really best suited to injecting liquids which are not necessarily the best way of delivering compounds to a patient and the fact that sharps are left which create a disposal problem.
Drug delivery systems that do not incorporate needles are also used for injecting liquids through the skin and this is achieved by the delivery system creating a very fine, high velocity liquid jet that creates its own hole through the skin. There are however a number of problems with such a method including splash back.
With both these forms of liquid delivery relatively large volumes of liquid are injected which, because they are incompressible, have to tear the tissue apart in order to be accommodated.
However, drug injection through the skin does not have to be achieved with the drug in a standard liquid form. Solid form drugs have been successfully administered with the PowderJect system, which uses a compressed gas source to accelerate powdered drugs to a velocity at which they can penetrate the outer layers of the skin. This system typically employs powdered drug particles of less than 100 microns in diameter, which require a velocity of several hundred meters per second in order to penetrate human tissue. However the system has its own inherent problems such as controlled delivery.
It has also been shown in the past that solid rods or splinters of a therapeutic compound can be pushed, at a relatively low velocity, into the skin without the requirement for a needle although more traditionally these are delivered as implants.
The current transdermal drug delivery techniques can thus be categorised into groups based on the drug form and the velocity of the injection as set out in table 1 below:
TABLE 1Drug FormDrug Injection VelocityLiquidSolidHigh VelocityLiquid Jet InjectorPowderJect SystemsDrug dartsLow VelocityNeedle and SyringeDrug ‘Splinters’
Drug darts are disclosed in a number of publications. WO 96/40351 (American Cyanamid) discloses an implant dart with a head of a solid plastics material which takes the form of a blade and a tubular body that contains one or more sustained release drug delivery implant packages. Flexible stabilizing wings are provided on either side of the dart head which serve as a lock or barb to prevent the dart being pulled out after entry. The dart has on outside diameter of about 7 mm and a length of about 45 mm and is delivered with an injection gun which fires the dart into an animal, but not a human, when a trigger is released. The propulsion mechanism delivers a force sufficient to impart a high accelerating velocity of from 40-60 mph on the dart. To inject the dart at low speed it is necessary to make a small incision in the animal and operate the push bar manually.
U.S. Pat. Nos. 3,948,263 and 4,326,524 also disclose ballistic delivery devices. U.S. Pat. No. 3,948,263 discloses a ballistic implant which is fired from a 0.25 calibre rifle. The projectile exits at about 900 ft/sec and can travel 20-40 ft before implanting into muscle some 1-2 inches beneath the skin. U.S. Pat. No.4,326,524 discloses a solid dose ballistic projectile formed entirely of a cohesive mixture comprising biologically active material, in the form of grindable solid particles and a binder which is capable of withstanding the stresses imparted on impact. The projectile has a body portion with a diameter of from 4.5 to 7.6 mm, with a conical nose portion with a base diameter smaller than the diameter of the body such that a slight shoulder region is formed between the body and the nose. The end remote from the nose is preferably concave to aid flight.
GB 2365100 is another example of a remote ballistic delivery device which is fired and attains velocities of greater than 500m/s. In contrast to those described above the device is slowed on impact so that it does not enter the body but instead the device's nose is moved back such that a needle enters the body, and a drug is injected. Such a device is not needleless.
CA1019638 discloses a projectile which is launched by a conventional air gun or bow. It comprises a head piece and a shaft, the head piece pierces the animals flesh and the shaft breaks away. In one embodiment the head piece is made of a porous material which retains a liquid drug through capillary action through launch and impact and which releases it by diffusion when it is inserted into the animal. In a second embodiment the head piece takes the form of a hardened cake. To aid penetration a metal or plastics tip may be provided. The drug delivering element remaining in the skin is about 3 mm diameter by 13 mm in length.
U.S. Pat. No. 3,901,158 Ferb discloses a hypodermic projectile which is again fired from a rifle or pistol. It comprises a shatterable front end of plastic or glass which breaks on impact releasing the liquid contents.
None of the described high velocity devices bear any resemblance to the present invention in which the at least one therapeutic compound or a formulation comprising the at least one therapeutic compound is pushed at low velocity from a device which contacts the skin and in which the pioneer projectile is water soluble, lipid soluble or otherwise biodegradable in the human or animal and is furthermore significantly smaller having a width or diameter of less than 3 mm in width, more preferably still less than 2.5 mm through 2 mm and 1.5 mm to about 1 mm in width; a height of less than 10 mm in height, more preferably about 1.5 to 2 mm in height and an aspect ratio of less than 1:8, preferably less than 1:6, more preferably less than 1:4, more preferably still less than 1:3, and most preferably about 1:1.5.
High velocity liquid systems are exemplified by U.S. Pat. No. 116,313 Mc Gregor. Liquid is first ejected from a small orifice in a probe at a very high velocity and pressure which will penetrate the skin and then the main charge of liquid is ejected at a lower velocity into the channel formed by the initial penetration.
EP0139286 (Sumitomo Chemical Co Limited) discloses sustained-release preparations in the form of needle like or bar like shapes, which comprise an active ingredient and a pharmaceutically acceptable biodegradable carrier. The sustained-release preparation can be administered to the body by injection by pushing it through a hollow needle or by implantation.
WO 94/22423 (Bukh Meditec AIS) discloses a drug administration system. The method of parenteral administration comprises administering a drug substance by penetrating the skin or the mucosa of a human or an animal by a body with an appropriately formed solid pharmaceutical composition. The body of the pharmaceutical composition may be needle shaped so as to avoid external penetration equipment. The solid pharmaceutical composition comprises at least one drug substance and has a shape and/or strength to enable penetration. The composition is made by mixing a material, preferably a polymer and optionally a filler with an active drug substance; extruding the mixture to form an elongate body; drying it and forming a pointed end.
U.S. Pat. Nos. 5,542,920, 6,117,443 and 6,120,786 (Cherif Cheikh) all disclose needle-less parenteral introduction devices. A medicament is made in the form of a solid needle having a pointed end that has sufficient structural integrity to penetrate the skin. The needles are less than 2 mm, preferably 0.2 to 0.8 mm, in diameter and 10 to 30 mm in length.
U.S. Pat. No. 6,102,896 (Roser) is primarily directed to a disposable injector device for injecting controlled release water soluble glass needles. It however also recognises that these glass needles, which are about 1 mm in diameter by 10 mm in length and contain a medicament may also be used as pioneer projectiles to produce a low resistance pathway through the tissue along which a liquid suspension (exemplified as a drug in a suspension of PFC fluid) can flow. This document appears the first and only document to recognise that a dissolvable pioneer projectile may be used to enable the introduction of a medicament. It however fails to recognise that it may be used as a general technique for introducing medicaments in other forms. Indeed this is readily apparent from the document in which a dry powdered formulation is made into a non viscous liquid by suspending it in PFC.